Amphibious aircraft

ABSTRACT

Described are aircraft with at least one fuselage, a wing, and at least one float coupled to the wing. As examples, each float may include a step that is located forward of or at an intersection of a bottom surface and a line that extends from an aircraft aft-most center of gravity at an angle of less than ten degrees rearward from a vertical direction As further examples, each float may include a forward portion located forward of the step, the forward portion including a ski surface that is slanar in a left to right horizontal direction, and an aft portion that is located rearward of the step.

FIELD OF THE INVENTION

The invention relates to amphibious aircraft, and more particularly toamphibious aircraft having twin stepped floats that enhance performanceboth on the water and in the air.

BACKGROUND

Seaplanes are aircraft that are capable of taking off and landing uponwater. Seaplanes may fall into two broad categories. In the firstcategory, the lower part of the fuselage is shaped like a boat hull andwhich, at rest and at low speeds, floats on the surface like a boat. Thesecond category consists of conventional land planes that are mounted onfloats in place of, or in addition to, conventional landing gear, whichare often referred to as float planes.

A seaplane that is also equipped with wheels is called an amphibian: anairplane capable of operating on land or water. An amphibian aircraft isdesigned to operate on unimproved runways and water and is an effectiveform of transportation into remote and undeveloped areas. Amphibianstypically include a pair of floats with landing gear that can beretractable or nonretractable. For operating on land, amphibians mayinclude a conventional landing gear design having a pair of main wheelsand a tailwheel. This type of landing gear may be preferable foramphibians operating in remote areas because this type of landing gearcan be better for unimproved field operation. Other types of amphibiansutilize a tricycle landing gear design, also known as a “nosewheel” typeof landing gear, which includes a pair of main wheels located on eachside of a centerline behind the plane's center of gravity, with anosewheel mounted on centerline forward.

For operating on water, float planes and amphibians typically utilize afloat shape that stabilizes the aircraft in water, yet does notsignificantly impede the aircraft's performance in the air. Earlierfloat designs tended to rely more heavily on displacement than planingat higher speeds, thus to some extent impeding takeoff ability. Oneanswer to this problem included providing a step so that at higher speedon the water, the wetted surface of the float was lower, and moreforward. A conventional float shape is often described as a planing tailbecause it only has one step with a forebody ahead of the step and anafterbody behind the step and a V-shaped bottom surface to reduce waterimpact loads. Many conventional float designs place the step atapproximately the same position as one would mount the main landinggear.

The location of the main landing gear for land-based aircraft, andconsequently the conventional location of the step for aircrafts, isdetermined on factors that include location of the most aft center ofgravity (“c.g.”). For example, in the tricycle landing gear design, thelanding gear main wheels are positioned behind the c.g. so that atrelevant portions of the aircraft performance envelope, the center ofgravity remains ahead of the main wheel contact point. Additionally, themain gear can be disposed at a trailing angle relative to the ground togive the aircraft inherent dynamic stability on the ground. In somecases, the main gear can be located at a trailing angle measured from avertical line passing through the c.g. or near the c.g. This angle canrange from 5° to 7° or more for some designs, for example, but may behigher or lower depending on a number of factors.

For amphibians with rectractable landing gear, the location of the stepat approximately the same position as one would mount the main landinggear causes the main landing gear to be located further aft than thedesired location described above. A further aft main landing gearposition may result in longer takeoff runs or more abrupt takeoffs onland because the further aft position of the landing gear makes it moredifficult to rotate the aircraft on takeoff. The greater difficulty inmaneuverability is due in part to the longer distance between the mainlanding gear and the c.g., which results in a higher moment needed forrotation, in turn requiring more elevator deflection, more airspeed, orboth, before the aircraft can be rotated to the proper angle of attackfor lift-off.

Locating the step in the conventional location for the main wheels alsointroduces negative handling characteristics on water that requireconstant pilot input after touchdown because the float plane oramphibian is balancing on the floats until the floats transition fromplaning mode to displacement mode. In effect, handling a float plane oramphibian with a conventionally located step after touchdown can bedescribed as analogous to balancing a broomstick on one's fingertips.

In some instances, seaplanes may also land and takeoff from surfacessuch as snow, wet grass, marshy areas or other unimproved surfaces. Inan emergency, these planes may be required to land and takeoff on soilor even pavement. In these situations, the conventional V-shaped bottomhas a tendency to dig into the surface, impeding the ability of theaircraft to separate from the surface on which it is moving.

Typically, smaller seaplanes include a propeller power plant that iseither forward- or aft-mounted. Forward-mounted propeller power plants,as known as tractor propellers, have the engine and propeller mounted atthe front of the aircraft where the thrust draws or pulls the airplane.Tractor propellers in seaplanes can send excessive spray over thecockpit and are more susceptible to bird collisions in areas thatpresent such a hazard.

Aft-mounted propeller power plants, as known as pusher propellers,feature propellers mounted behind the engine where the thrust producedby the propeller pushes the airplane forward. Pusher propellers canoffer better visibility and less drag than tractor configurations, buttend to reduce wing lift at the higher angles of attack associated withshort-field takeoff, as well as during abrupt power corrections in theapproach or landing configuration. Typically, maintenance concerns havefavored tractor propellers because pusher propellers are subject todamage from turbulent flow, materials coming from the cabin, loosehardware left inside the cowling, and debris thrown up by the landinggear.

In either configuration, open-design propellers create a substantialamount of noise and can be less efficient than propellers rotatingwithin a shroud, which reduce tip effect loss.

Accordingly, there is a need for a seaplane or amphibious design thatimproves the location of the step and landing gear for improved handlingduring takeoff and landing on both land and water. There is also a needto provide a float shape that enables efficient separation of theaircraft from the water and allows the aircraft greater flexibility totakeoff and land on a variety of surfaces. Moreover, there is a need fora seaplane or amphibious aircraft design featuring a shrouded pusherpropeller power plant design with improved visibility, less drag,improved thrust performance at static and low speeds for short-fieldtakeoffs, reduced likelihood of damage during operation, and quieteroperation.

SUMMARY

Embodiments of the present invention include an aircraft with at leastone fuselage, a main wing, a propeller power plant coupled to the atleast one fuselage, a shroud surrounding the propeller, and at least twofloats coupled to the wings. In some embodiments, each float may furthercomprise a step positioned forward of a line that is at least 5 degreesrearward of a vertical line passing through a most aft or other desiredcenter of gravity. In other embodiments, the step is positioned betweenthe vertical line passing through the most aft empty weight center ofgravity and the line that is angled at least 5 degrees rearward of thevertical line. In yet other embodiments, the step is positioned on thevertical line passing through the most aft empty weight center ofgravity.

In some embodiments, each float comprises a forward portion that ispositioned forward of the step, wherein a ski surface forms part of thebottom of the forward portion, and an aft portion that is positioned aftof the step, wherein the aft portion of each float is wetted at taxiingspeed so that the aircraft operates has the feel on water more similarto how a “tail dragger” or aircraft with conventional gear designoperates on land. A rudder may be coupled to the aft portion to enablesteering while taxiing on the water. Each float may also include aretractable wheel and landing gear, wherein the wheel is preferablylocated on a line that is at least 5 degrees rearward of a vertical linepassing through the most aft empty weight center of gravity.

The aircraft may take off from water by first operating in a taxiingregime, with nose-high trim when taxiing, accelerating the aircraftabove taxiing speed to transition the aircraft to a planing regime onthe forward portion of each float so that the aft portion is no longerwetted, reaching takeoff speed, and causing the aircraft to fly orrotate off the water as desired.

The aircraft may land on water by decelerating the aircraft to desiredlanding speed, configuring the flaps and the aircraft otherwise forlanding, contacting the forward portion of each float with the watersurface, and allowing the aft portion of each float to drop and becomewetted, whereupon the floats operate in a displacement mode for taxiing,without undue time spent having to “fly the plane on the water” thatwould otherwise be necessitated by conventional float designs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an amphibious aircraft according to oneembodiment of the present invention.

FIG. 2 is a side view of the amphibious aircraft of FIG. 1.

FIG. 3 is another side view of the amphibious aircraft of FIG. 1.

FIG. 4 is a front elevation view of the amphibious aircraft of FIG. 1.

FIG. 5 is a perspective view of the float of the amphibious aircraft ofFIG. 1 with the wheel retracted.

FIG. 6 is a side view of the float of the amphibious aircraft of FIG. 1with the wheel extended.

DETAILED DESCRIPTION

FIGS. 1-6 illustrate an amphibious aircraft 10 according to oneembodiment of the invention. In this embodiment, the aircraft 10features a power plant 12 mounted to an aft portion of fuselage 14. Thefuselage 14 includes a wing 16. A float 18 is cantilevered from the wing16. A vertical fin 20 is coupled to the aft end of each float 18. Ahorizontal stabilizer 22 is coupled to the vertical fins 20, preferablybut not necessarily near the top of the fins 20, to complete a tailportion 24. A nosewheel 26 is coupled to the front of the fuselage 14.

In some embodiments, the fuselage 14 is configured for appropriatehydrodynamic effects, both statically and dynamically during all phasesof taxiing, takeoff, and landing. The fuselage 14 may feature anydesired shape, length, width, and height to accomplish the result ofappropriate aerodynamic and hydrodynamic performance for a generalaviation class amphibious aircraft with favorable stability, airspeed,range, and maneuverability characteristics. The fuselage 14 may beassembled in a stress skin monocoque, semimonocoque, or longitudinalmember design, or a combination of any or all of these designs. A skin27 is fastened to the design and carries primarily the shear load,tension, and bending stresses. The fuselage 14 may be formed of anysuitable material including but not limited to aluminum, aluminumalloys, other metallic materials, composite materials, or other similarmaterials. The horizontal stabilizer 22 may be included as shown inFIGS. 1-4. The horizontal stabilizer 22 generally affects pitchperformance during taxiing, takeoff, and landing on the water.

The wing 16 can formed of a stress skin monocoque, semimonocoque, orconventional longitudinal member design, or a combination of any or allof these designs. A monocoque construction can use corrugationsextending along the length of the wing 16 for structural integrity. Incross section, the corrugations provide advantages of a warren trussarrangement, which provides stability and stiffness for the wing 16. Thewing 16 may be formed of any suitable material including but not limitedto aluminum, aluminum alloys, other metallic materials, compositematerials, or other similar materials.

FIGS. 1-6 illustrate one embodiment of the float 18, which includes astep 28 and a main wheel 30. The float 18 may be formed of any suitablematerial including but not limited to stress skin monocoque, wood, foam,plastic, composites, fiberglass, or other desired materials. The floats18 are oriented substantially parallel to chords of the wing 16. As aresult, the floats 18 present minimal surface area to the airflow, thusreducing drag and increasing cruise speed of the aircraft 10.

The step 28 divides the float 18 into a forward portion 32 and an aftportion 34. In some embodiments, the forward portion 32 is shaped toincorporate a ski surface 36 into a bottom 38 of the float 18. In theseembodiments, the ski surface 36 results in a float 18 having a lowersurface that is generally planar. The ski surface 36 provides the float18 with improved planing capabilities, allowing earlier transition tothe planing mode and thus increasing acceleration and decreasing thetime spent on the surface during take-off. In some embodiments, theincorporation of the ski surface 36 significantly enhances take-offperformance compared to that of a more conventionally arranged floatshape. For example, the incorporation of the ski surface 36 may providetakeoff speeds of substantially 52 knots, more preferably between 52 and56 knots, which is substantially higher than takeoff speeds forconventionally located steps, where conventional takeoff speeds rangefrom 35 to 39 knots. The use of the ski surface 36 may also allow theaircraft 10 to takeoff from distances less than 1000 feet. Due to itsplanar configuration, the ski surface 36 enables lower surface contactpressure, resulting in less friction or tendency of the float 18 tobecome entrenched in the landing surface, particularly when the landingsurface is snow, wet grass, or marginal environments such as marshyareas or when landing in soil or pavement during an emergency.

In some embodiments, as shown in FIGS. 2, 3, 5, and 6, the step 28creates a sudden break or discontinuity in the longitudinal linesextending from the forward portion 32 at the approximate point aroundwhich the aircraft 10 rotates into a lift-off attitude. The step 28allows water to flow freely behind the step, resulting in minimumsurface friction to allow the aircraft 10 to break away from the water'ssurface. In some embodiments, the step 28 is located slightly forward ofa conventional step location, where the conventional location isrearward 6° to 10° off a vertical c.g. location 40. The c.g. location 40may have any appropriate location on the aircraft 10 based on thevarious components and loading parameters associated with the aircraft10. In one embodiment, as illustrated in FIG. 3, the step 28 is locatedon a vertical line passing through the c.g location 40. In otherembodiments, the step 28 is located between a vertical line passingthrough the c.g. location 40 and the conventional location.

In the embodiments where the step 28 is located forward of itsconventional location, the aft portion 34 of the float 18 is in thewater at taxiing speeds, whereupon the floats 18 are acting in adisplacement mode, the aircraft has a nose up trim, and a pair ofrudders 44 can be used to steer. The forward shift of the step 28 movesthe float's resultant pressure vector slightly forward of the moreconventional location. As a result, the aircraft's resultant forcevector is similar to the configuration of a “tail dragger” land plane,where a tail dragger is a term used to describe a type of conventionallanding gear for land planes where the main wheels are located on eachside of the centerline ahead of the c.g., with a steerable tailwheellocated under the tail. This type of landing gear is known for itsability to land “tail first.” However, unlike the tail dragger landplane, which may incur momentum-caused handling issues, the waterenvironment for the aircraft 10 will actually aid the handling andstability characteristics by providing a stabling and damping influenceon an aft portion 42. Hence, the aircraft 10 operates as a “taildragger” when the aft portions 34 are wetted. This configuration causesthe aircraft 10 to sit in nose-high trim when taxiing, but allows anearly ideal take-off attitude with little or no input from the pilot.

During take-off, as the aircraft 10 transitions toward takeoff speed,the aircraft 10 begins to plane on the forward portion 32 of each float18, so that the aft portion 34 of each float 18 is no longer wetted. Theforward portion 32 of each float 18 acts as a hydroplane so that theaircraft 10 can be flown off the water straight and level. Theaerodynamic center of the wing 16 and the horizontal stabilizer 22 liftthe aft portions 34 off the water, so that the center of buoyancy shiftsforward from aft of the c.g. to a more forward location, which isforward of the step 28. Because the aircraft 10 operates as a taildragger during takeoff on water, the aircraft 10 can maintain arelatively stable angle of attack throughout its acceleration run, withonly minimal input from the pilot required. Properly trimmed andconfigured, it is possible that the aircraft 10 will be able toaccelerate and lift off the water with no pilot input, beyond moving thethrottle to takeoff position.

In some embodiments, the forward location of the step 28 significantlyenhances take-off performance compared to a more conventionally locatedstep. For example, the forward location of the step 28 may allow takeoffspeeds of substantially 52 knots, preferably between 52 and 56 knots,which is substantially higher than conventional takeoff speeds of 35 to39 knots. The forward location of the step 28 may also allow theaircraft 10 to takeoff from distances less than 1000 feet.

When landing the aircraft 10, the same tail dragger-like float 18configuration allows the tail portion 24 to settle into the waterearlier and with less pilot input, accomplishing on-water stability thatis not possible with a more conventional float design. In short, thepilot does not have to fly the plane on the water down to taxi speed asis the case for conventional float designs, thus reducing the potentialfor noseovers. The tendency to settle the tail portion 24 quickly isconsidered to be more stable and thus safer because of the shiftedbalance position. It is possible that the aircraft 10, with correct trimsettings, will be able to land and transition to displacement mode withlittle or no pilot input.

When performing a takeoff or landing on land, the aircraft 10 operateslike a land plane with tricycle gear because the main wheels 30 arelocated in the conventional location (i.e., not located aft of thepreferred 6° to 10° off the vertical c.g. location). Therefore, handlingof aircraft 10 on a hard runway is no different than any other tricycleconfigured plane. The similarity of runway characteristics allows foreasier pilot transition from a conventional land aircraft to theaircraft 10.

To maneuver the aircraft 10 in the water, some embodiments include therudder 44 that is positioned on the aft portion 34 behind the step 28,which is illustrated in FIGS. 2, 3, 5, and 6. When the aircraft 10planes on the forward portion 32 of each float 18, the rudder 44 isremoved from the water. Due to its placement behind the step 28, therudder 44 does not create any drag and therefore does not requireretraction during flight. In some embodiments, the rudder 44 is locatedapproximately three-quarters of the distance between the step 28 and theaft end 42 of the float 18 in a direction toward the aft end 42. Therudder 44 may be formed of any appropriate material including but notlimited to aluminum, carbon steel, stainless steel, other metallicmaterials, composite materials, or other similar materials. The tendencyto quickly settle the tail portion 24 is considered to be more stableand thus safer because it allows the rudders 44 to function sooner thanwhat might otherwise be possible with a conventional step location.

In some embodiments, as shown in FIGS. 1-4, the power plant 12 includesa reciprocating propeller/fan design. In some embodiments, the powerplant 12 is an aft-mounted propeller power plant 12. However, the powerplant 12 may be mounted in any suitable location and may be of anydesired manufacture or design, including reciprocating or jet. The fanor propeller (in this document, both are included in the meaning of theterm “propeller”) may be constant speed or variable speed, controllablepitch or otherwise. One particular form of power plant design that isappropriate is a fanjet or jet engine with high bypass ratio. Theaft-mounting location provides some protection to the power plant 12from excessive spray during water landings and takeoffs.

In some embodiments, as shown in FIGS. 1-4, the power plant 12 is apropeller power plant wherein the propeller is surrounded by a shroud46. The shroud 46 can substantially enhance efficiency and performanceof the propeller, can make the propeller/power plant combinationquieter, and can provide additional protection to prevent contactbetween the propeller power plant 12 and the water. The shroud 46 alsoprotects the propeller power plant 12 from damage caused by objects thatit would otherwise encounter.

The shroud 46 may be formed of any suitable material including aluminum,carbon steel, stainless steel, other metallic materials, compositematerials, or other similar materials. The shroud 46 can either be wipedby the propeller or provide sufficient space for the propeller to rotatefreely. In cross section, the shroud 46 may be any appropriate shapethat reduces drag and gives appropriate performance characteristics,including but not limited to an airfoil with the high-pressure sidefacing outward, an airfoil with the high-pressure side facing inward, orany other appropriate shape.

At low airspeeds, the shrouded propeller power plant 12 increases thestatic and low speed thrust performance over an open propeller powerplant of the same diameter. Thus, the static and low speed thrust isincreased without any change in power or power plant diameter. Theimproved performance of the shrouded propeller power plant 12 reducesthe required take-off distance and increasing climb rates. Thisincreased power plant effectiveness continues through cruising speeds inexcess of 200 knots.

The shroud 46 also reduces the amount of noise produced by the propellerpower plant 12. As a result, the shrouded propeller power plant 12produces a quieter operation as compared to open propeller power plantconfigurations. The aircraft 10 is therefore able to operate within morenoise sensitive areas such as those with higher population densities orforms of environmental noise restrictions.

The foregoing is provided for purposes of illustrating, explaining, anddescribing embodiments of the present invention. Further modificationsand adaptations to these embodiments will be apparent to those skilledin the art and may be made without departing from the scope or spirit ofthe invention.

1.-32. (canceled)
 33. An aircraft configured to take off and land onwater, the aircraft including at least one fuselage and at least onewing connected to the fuselage, the aircraft including an aft-mostcenter of gravity and at least one float, the float comprising: a floatbody that includes a bottom surface; a bottom surface forward portionlocated on the float body bottom surface, the bottom surface forwardportion including a ski surface that is planar in a left-to-righthorizontal direction; a bottom surface rearward portion located on thefloat body bottom surface, the bottom surface rearward portion includinga rudder; and a bottom surface step located on the float body bottomsurface and interposed between the bottom surface forward portion andthe bottom surface rearward portion, the step including a point that islocated forward of or at an intersection of the bottom surface and aline that extends from the aircraft aft-most center of gravity at anangle of less than ten degrees rearward from a vertical direction. 34.An aircraft according to claim 33, wherein the step includes a pointthat is located forward of or at the intersection of the bottom surfaceand a line that extends from the aircraft aft-most center of gravity atan angle greater than six and less than ten degrees rearward from thevertical direction.
 35. An aircraft according to claim 33, wherein thestep includes a point that is located forward of or at the intersectionof the bottom surface and a line that extends from the aircraft aft-mostcenter of gravity at an angle of five degrees rearward from the verticaldirection.
 36. An aircraft according to claim 33, wherein the at leastone float includes a center of buoyancy on a line extending verticallyfrom the aircraft aft-most center of gravity and rearward of the bottomsurface step when the aircraft is at rest on the water.
 37. An aircraftaccording to claim 33, wherein the at least one float includes a centerof buoyancy that is located forward of the bottom surface step duringtakeoff of the aircraft.
 38. An aircraft according to claim 33, whereinthe at least one float is connected to the at least one wing.
 39. Anaircraft according to claim 33, wherein the aircraft includes twofloats.
 40. An aircraft according to claim 33, wherein the at least onefloat includes at least one landing gear.
 41. An aircraft according toclaim 40, wherein the at least one landing gear includes at least onewheel.
 42. An aircraft according to claim 33, wherein the float bodyincludes a nose and the ski surface includes a convergent portionwherein a pair of edges of the ski surface converge toward the nose ofthe float body.
 43. An aircraft according to claim 42, wherein at leastpart of the bottom surface forward portion is concave in cross section.44. An aircraft according to claim 43, wherein at least part of thebottom surface forward portion includes a pair of streamline surfacesthat are concave in cross section adjacent the ski surface convergentportion.
 45. An aircraft configured to take off and land on water, theaircraft including at least one fuselage and at least one wing connectedto the fuselage, the aircraft including an aft-most center of gravityand at least one float, the float comprising: a float body that includesa bottom surface and a nose; a bottom surface forward portion located onthe float body bottom surface, the bottom surface forward portionincluding: a ski surface that is planar in a left-to-right horizontaldirection, wherein the ski surface includes a convergent portion towardthe nose of the float body; and a pair of streamline surfaces that areconcave in cross section adjacent the convergent portion of the skisurface; a bottom surface rearward portion located on the float bodybottom surface, the bottom surface rearward portion including a rudder;and a bottom surface step located on the float body bottom surface andinterposed between the bottom surface forward portion and the bottomsurface rearward portion, the step including a point that is locatedforward of or at an intersection of the bottom surface and a line thatextends from the aircraft aft-most center of gravity at an angle of lessthan ten degrees rearward from a vertical direction.
 46. An aircraftaccording to claim 45, wherein the step includes a point that is locatedforward of or at the intersection of the bottom surface and a line thatextends from the aircraft aft-most center of gravity at an angle greaterthan six and less than ten degrees rearward from the vertical direction.47. An aircraft according to claim 45, wherein the step includes a pointthat is located forward of or at the intersection of the bottom surfaceand a line that extends from the aircraft aft-most center of gravity atan angle of five degrees rearward from the vertical direction.
 48. Anaircraft according to claim 45, wherein the at least one float includesa center of buoyancy on a line extending vertically from the aircraftaft-most center of gravity and rearward of the bottom surface step whenthe aircraft is at rest on the water.
 49. An aircraft according to claim45, wherein the at least one float includes a center of buoyancy that islocated forward of the bottom surface step during takeoff of theaircraft.
 50. An aircraft according to claim 45, wherein the at leastone float is connected to the at least one wing.
 51. An aircraftaccording to claim 45, wherein the aircraft includes two floats.
 52. Anaircraft according to claim 45, wherein the at least one float includesat least one landing gear.
 53. An aircraft according to claim 52,wherein the at least one landing gear includes at least one wheel.